Saturday, March 28, 2015

A leap second is a one-second
adjustment that is occasionally applied to Coordinated Universal Time
(UTC) in order to keep its time of day close to the mean solar time.
Without such a correction, time reckoned by Earth's rotation drifts away
from atomic time because of irregularities in the Earth's rate of
rotation.

Description:

Why Do We Need Leap Seconds?

The
reason we have to add a second every now and then, is that Earth's
rotation around its own axis, is gradually slowing down, although very
slowly.Atomic clocks
however, are programmed to tick away at pretty much the same speed over
millions of years. Compared to the Earth's rotation – which determines
the length of a day – the atomic clocks are simply too accurate.Exactly how do Leap seconds work?

How Often Are Leap Seconds Added?

Did you notice? The last leap second was added at 23:59:60 UTC on June 30, 2012.
Since
1972, a total of 25 seconds have been added. This means that the Earth
has slowed down 25 seconds compared to atomic time since then.
This
does not mean that days are 25 seconds longer nowadays. Only the days
on which the leap seconds are inserted have 86,401 instead of the usual
86,400 seconds.